1. Field of the Invention
The invention relates generally to power subsystems for downhole equipment such as electrical submersible pumps (ESP's), and more particularly to means for making robust connections between power system components the downhole equipment.
2. Related Art
Downhole equipment such as ESP systems are commonly installed in wells for purposes of producing fluids (e.g., oil) from the wells. Power suitable to drive the equipment is produced at the surface of the wells and is delivered to the equipment via power cables that extend into the wells. The power cables may have one or more electrical junctions, such as splices to motor leads and “pothead” connectors that couple the power cable to the downhole equipment.
It is very common in conventionally designed electrical junctions that fluids (e.g., oil and well fluids) will be introduced into the junctions. For example, in a conventional pothead connection between a power cable and an ESP motor, a pothead connector is connected to terminal conductors that extends through an insulation block (an “i-block”) in the motor head. The i-block is designed to allow oil from the motor to flow between the i-block and the motor head, thereby filling any open spaces within the junction of the pothead connector and the motor terminals. As the motor is operated, small debris particles in the oil may accumulate at the pothead junction, eventually causing short-circuits between different conductors within the junction and corresponding power failures. The same fluid paths that allow oil to flow out of the motor and into the pothead connection may also allow well fluids to leak into the motor, contaminating the oil in the motor and degrading its performance.
There are other types of problems with conventional electrical junctions as well. For example, cable splices are typically made using tape splicing materials, or in some cases mandrel-type splices. In the case of a tape splice, the metal armor and electrical insulation are peeled back from the conductors of to cable ends and, after the conductors are spliced, the junction is wrapped with electrically insulating tape to provide electrical insulation, and then polytetrafluoroethylene (PTFE) tape to provide some hoop strength. The metal armor is then replaced. The problem with this type of splice is that the electrical splicing tape and PTFE tape are organic, elastomeric materials that are subject to wear and subsequent failure in the well environment. In the case of mandrel-type splices, mechanical connectors are coupled to a mandrel to make the splice, but rubber boots, electrical tape or other, similar organic/elastomeric materials were typically used at the coupling of the connectors to the cable, so these materials are subject to wear in the same manner as tape splices.
It would be desirable to provide improved means for making electrical connections between downhole equipment such as ESP motors and their respective power supplies, wherein the connections are more robust than conventional electrical connections and can withstand wear in the well environment, as well as high pressures, high temperatures, and high mechanical stresses.